The invention relates in general to garage door operators and in particular to a jack shaft garage door operator having a pivoting arm for preventing cable associated with a pull-up cable drum from becoming slack during the operation of the door and for providing a positive door locking system.
One of the problems associated with jack shaft garage door operators is that while they are compact and may be conveniently used in garages which have little overhead room, they may present problems to the owners of the garage in that the cable may be payed out allowing the door to close under its own weight and if the door stalls or if the cable pay out drum rotates too far, the tension in the cable will drop and the cable may come off the drum necessitating a visit from a repairman.
In addition, the jack shaft garage door operator does not provide any secure locking facility other than a lock at the bottom of the door, which may be tampered with by a burglar. If the door is not locked by some other means, the bottom lock may be forced or damaged and the door can be lifted open and the garage entered by an intruder.
U.S. Pat. No. 3,785,809 discloses a door operator having a winch member built into a tilting door and movable with it. A cable is attached to a wall member supporting the door and another end of the cable is connected to an extensible arm.
U.S. Pat. No. 2,185,828 discloses a catch for stopping a door from falling in the event that a sustaining cable or a counterbalance fails or breaks.
U.S. Pat. No. 4,385,471 discloses a door including a stopping member having a clip connection 29 which engages a cable. If the cable breaks, as shown in FIG. 4, the arm 27 rotates outwardly bringing a cam dog 26 having a plurality of teeth 32 into locking engagement with a roller 13a to prevent the roller 13a from moving, thereby suspending the door in position.
U.S. Pat. No. 4,520,591 to Calvagno discloses a system that is mechanically responsive to a break in a cable to prevent a door from falling.
French Patent No. 2634-815-A includes an “antidrop” safety mechanism having a cam plate 21 on either side of the door equipped with a convex toothed edge to engage a bracket in case of door suspension failure. None of the aforementioned documents teach or disclose solutions for preventing a door from being opened or from stopping an operation of a garage door operator to cause it to reverse to take up cable which may have inadvertently been payed off a cable drum of a jack shaft door operator.
What is needed then is an improved jack shaft garage door operator that avoids unwanted problems with the cable coming off the drum and provides security for the user.